What Causes Muscle Growth? Here Are the Real Mechanisms

And Busting The Myth Of Muscle Damage 

"How does muscle growth occur?" is one of the most misunderstood topics in strength training.

For decades, lifters have believed that muscle growth comes from breaking down the muscle. You then used muscle soreness, or DOMS, to measure if your workout was good.

Many lifters still believe this. However, research has actually shown this to not be true; the real drivers of hypertrophy are mechanical tension and metabolic stress from consistent, progressive overload.

In this article, we break down what actually causes muscles to grow, why soreness doesn't matter, and how to train for real results without breaking down your body.

How Does Muscle Growth Occur?

Muscle growth ultimately occurs when the muscle is stressed, which triggers various anabolic processes. These processes signal the muscles to adapt to the new stimuli, i.e., build bigger and stronger muscles.

The primary way this hypertrophy occurs is through resistance training, but it can also result from any type of demanding work. Essentially, you cause your body to adapt to its surroundings.

With this in mind, continual muscle growth requires using progressive overload. Progressive overload is the most critical training principle, which simply says that for a muscle to grow, a gradual increase in stress must be placed on it over time (Plotkin et. al, 2022).

Progressive overload = adding stress over time through more load, more reps, more sets, or increasing intensity. Basically, do more work.

Without increasing stress, the body has no reason to adapt.

What Are The Main Mechanisms Of Muscle Growth?

The main mechanisms of muscle growth are mechanical tension, metabolic damage, and, to a lesser extent, muscle damage. Of these three, muscle tension and metabolic damage are the primary mechanisms of muscle growth (Schoenfeld et. al, 2010).

1. Mechanical Tension (Primary)- The force a muscle produces under load, especially when trained close to failure, and is the primary stimulus that drives hypertrophy (Behringer et. al, 2025).

2. Metabolic Stress (Secondary) - he buildup of metabolites like lactate during hard sets, creating the pump and burn that supports but does not replace mechanical tension–driven growth (de Freitas et. al, 2017).

3. Muscle Damage (Not a driver) - Micro-trauma that occurs from novel or excessive training, but it does not stimulate hypertrophy and is not required for muscle growth (Behringer et. al, 2025).

How Does Mechanical Tension Cause Muscle Growth?

Mechanical tension is the force generated by a contracting muscle. This is where the general idea of Time Under Tension came from. This is optimized through;

• Heavy loads
• Lengthened positions
• Controlled tempos
• Sets taken near failure

When the muscle senses mechanical tension, it activates various pathways that stimulate:

• mTOR signaling
• Satellite cell activity
• Muscle protein synthesis
• Fiber remodeling (Gordon et al., 2014; Hornberger, 2011)

To ensure optimal mechanical tension is applied, perform reps smoothly and with control. However, you do not need to deliberately perform extra-slow reps.

You then apply progressive overload. This is the main stimulus for muscle growth.

How Does Metabolic Damage Cause Muscle Growth?

Metabolic stress refers to the buildup of metabolites (lactate, H+, phosphate) that occur during hard training (de Freitas et. al, 2017). This creates the "burn" or "pump" when lifting. The accumulation of metabolites results in;

• Increases cell swelling
• Enhances hormonal signals
• Recruits high-threshold motor units when fatigued

This explains why BFR (blood flow restriction) works: it results in pooling of blood and metabolites.

Metabolic Damage is one of the primary reasons it's important to train with intensity. 

Does Muscle Damage Cause Muscle Growth?

No, muscle damage does not cause muscle growth. In fact, it's not even necessary to occur (Behringer et. al, 2025). This is one of the most misunderstood aspects of resistance training and bodybuilding.

Muscle damage is not required for hypertrophy, and does not predict gains.

A large part of the confusion stems from misinterpretations of previous research. Muscle Protein Synthesis (MPS) can increase during muscle repair and muscle growth.

However, MPS that repairs muscles is not the same as muscle hypertrophy. Consider this;

• Muscles grow through anabolic processes during puberty
• Muscle damage and DOMS decrease as lifters become more advanced 
• Levels of muscle damage and muscle hypertrophy have been found to have minimal correlation 

Key Research To Know About Muscle Damage

A. Damage is highest in beginners, but doesn't improve growth

Damas et al. (2016) showed that untrained individuals experience high markers of muscle damage early in their training. However, as they continue training, damage decreases even though hypertrophy continues.

B. Damage markers do not correlate with muscle growth

Schoenfeld (2012) concluded that muscle damage may play a role in hypertrophy, but it is not necessary for hypertrophy. Furthermore, excessive emphasis may impair performance.

"There is a sound theoretical rationale supporting a potential role for (muscle damage) in the hypertrophic response. Although it appears that muscle growth can occur in the relative absence of muscle damage."

C. New 2025 research confirms the same

Behringer et al. (2025) conducted an extensive review of the literature and found no evidence that muscle damage contributes significantly to hypertrophy.

"While muscle damage may contribute to hypertrophy, it is not a necessary condition for muscle growth. Other mechanisms, such as mechanical tension and metabolic stress, play more central roles in promoting hypertrophy."

Is Muscle Soreness Needed For Muscle Growth?

Muscle soreness is not required for muscle growth, and it is not a reliable indicator of how effective your training was. Soreness mainly reflects novelty, not hypertrophy.

You get sore when you expose the muscle to something unfamiliar, such as a new exercise, a deeper range of motion, a sudden increase in volume, or eccentric-dominant work.

What the research shows:

• Soreness peaks when you first start training or introduce a new stimulus.
• As your body adapts to training, soreness will generally decrease, even though you can still build muscle.
• Damas et al. (2016) demonstrated that muscle damage and soreness drop significantly after repeated bouts, yet muscle growth remains steady.
• This shows that you do not need to "break down" your muscle to trigger muscle growth. 

Why soreness is not helpful as a guide:

• It reflects unfamiliar work, not effective tension.
• High soreness can actually reduce performance in your future training sessions.
• This can limit things like training frequency, total volume, and even progressive overload.
• Productive training requires training hard but allowing yourself to recover. This occurs in a cyclical manner. 

Step-by-Step Process Of Muscle Growth

• A training stimulus places mechanical tension on the muscle. 

Hard sets performed close to failure create high mechanical tension. This is the primary trigger for hypertrophy, which stimulates various mechanisms.

• Mechanical tension activates mechanosensors within muscle fibers.

These sensors detect the force being applied and convert it into biochemical signals inside the cell (mechanotransduction) (Gordon et al., 2014; Hornberger, 2011).

• Intracellular signaling pathways become activated.

Key anabolic pathways increase in response to the tension placed on the muscle.

• mTOR → increases protein synthesis
• MAPK/ERK → growth & adaptation
• FAK (focal adhesion kinase) → signals mechanical load
• YAP/TAZ → gene expression related to hypertrophy (Gordon et al., 2014; Hornberger, 2011)

• Muscle protein synthesis (MPS) is elevated above baseline.

The body begins producing new contractile proteins (actin and myosin) to reinforce the stressed fibers. MPS temporarily rises for several hours after training.

• Muscle protein breakdown (MPB) also increases, but to a lesser extent.

Exercise induces a short-term increase in MPB, but the net balance becomes positive when MPS exceeds MPB, especially with adequate protein intake (Damas et. al, 2015).

• Satellite cells become activated.

These muscle "stem cells" donate nuclei to existing fibers, allowing the muscle to support more protein turnover and grow larger over time.

• New myofibrils are formed, and existing ones become thicker.

Repeated cycles of elevated MPS increase myofibrillar protein content, leading to muscle fiber enlargement.

• Progressive overload reinforces and expands the adaptation.

As training stress gradually increases, the muscle continues to increase MPS and remodel itself. Over time, this results in long-term hypertrophy. You are essentially forcing your body to adapt.

Understanding Muscle Growth: Why It Matters

Knowing the mechanisms can affect your training methods and what you're trying to achieve in the gym. In the past, it was not uncommon to hear lifters say they needed to train hard and "break down their muscle". This gave birth to many training methods, such as drop sets and the mindset of  "No Pain, No Gain".

In reality, your focus is on putting quality tension on the muscle. Be sure to bring sets within failure proximity and increase work progressively, and you'll build muscle. 

FAQ About Muscle Growth

1. Do muscles need to be sore to grow?

No. Muscle soreness is not required for hypertrophy and does not correlate with growth. It mainly reflects novelty, not stimulus. (Damas et al., 2016)

2. Is muscle damage necessary for muscle growth?

No. Research consistently shows muscle damage does not drive hypertrophy and may even reduce performance if excessive. (Schoenfeld, 2012; Behringer et al, 2025)

3. What is the main driver of muscle growth?

Mechanical tension is the primary mechanism behind hypertrophy (Schoenfeld, 2010). This is essentially when a load is being placed on the muscle.

4. Does metabolic stress help build muscle?

Yes. Metabolic stress (the burn/pump) can enhance growth when paired with high tension (de Freitas et. al, 2017)

5. How important is progressive overload?

Essential. Non-negotiable. Progressive overload is the foundation of long-term muscle growth, and without it, your muscles have no reason to grow.

6. Can you grow muscle with light weights?

Yes. Loads as low as ~30% 1RM can still build muscle if sets are taken near failure, as it creates high tension and full motor-unit recruitment. This is useful for populations that are unable to use heavier loads.

7. Should every set be taken to failure?

It is not necessary to train to failure to build muscle, let alone every set. Training within 1–3 reps in reserve (RIR) can maximize tension while also managing fatigue (Martikainen et. al, 2025). Failure can be used sparingly, but isn't required.

References

1. Behringer, M., Heinrich, C., & Franz, A. (2025). Anabolic signals and muscle hypertrophy: Significance for strength training in sports medicine. Sports Orthopaedics and Traumatology, 41(Suppl 1). https://www.sciencedirect.com/science/article/pii/S0949328X2500002X
2. Damas, F., Phillips, S., Vechin, F. C., et al. (2015). A review of resistance training-induced changes in skeletal muscle protein synthesis and their contribution to hypertrophy. Sports Medicine, 45(6), 801–807. https://doi.org/10.1007/s40279-015-0320-0
3. Damas, F., Phillips, S. M., Lixandrão, M. E., Vechin, F. C., Libardi, C. A., Roschel, H., Tricoli, V., & Ugrinowitsch, C. (2016). Early resistance training-induced increases in muscle cross-sectional area are concomitant with edema-induced muscle swelling. European Journal of Applied Physiology, 116(1), 49–56. https://doi.org/10.1007/s00421-015-3243-4 
4. de Freitas, M. C., Gerosa-Neto, J., Zanchi, N. E., Lira, F. S., & Rossi, F. E. (2017). Role of metabolic stress for enhancing muscle adaptations: Practical applications. World journal of methodology, 7(2), 46–54. https://doi.org/10.5662/wjm.v7.i2.46 
5. Gordon, B. S., Kelleher, A. R., & Kimball, S. R. (2014). Regulation of muscle protein synthesis and the effects of catabolic states. International Journal of Biochemistry & Cell Biology, 45(10), 2147–2157. https://doi.org/10.1016/j.biocel.2013.05.039
6. Hornberger, T. A. (2011). Mechanotransduction and the regulation of mTORC1 signaling in skeletal muscle. International Journal of Biochemistry & Cell Biology, 43(9), 1267–1276. https://doi.org/10.1016/j.biocel.2011.05.007 
7. Martikainen, O., Niiranen, H., Rytkönen, T. et al. Influence of Varying Proximity-to-Failure on Muscular Adaptations and Repetitions-in-Reserve Estimation Accuracy in Resistance-Trained Individuals. J. of SCI. IN SPORT AND EXERCISE (2025). https://doi.org/10.1007/s42978-025-00338-8 
8. Plotkin, D., Coleman, M., Van Every, D., Maldonado, J., Oberlin, D., Israetel, M., Feather, J., Alto, A., Vigotsky, A. D., & Schoenfeld, B. J. (2022). Progressive overload without progressing load? The effects of load or repetition progression on muscular adaptations. PeerJ, 10, e14142. https://doi.org/10.7717/peerj.14142 
9. Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research, 24(10), 2857–2872. https://doi.org/10.1519/JSC.0b013e3181e840f3 
10. Schoenfeld, B. J. (2012). Does exercise-induced muscle damage play a role in skeletal muscle hypertrophy? Journal of Strength and Conditioning Research, 26(5), 1441–1453. https://journals.lww.com/nsca-jscr/fulltext/2012/05000/Does_Exercise_Induced_Muscle_Damage_Play_a_Role_in.37.aspx)